Dispersion type electroluminescent elements

ABSTRACT

In a dispersion type electroluminescent element comprising a pair of electrodes and an electroluminescent layer sandwiched between the electrodes and including an electroluminescent phosphor dispersed in an organic or inorganic binder, the luminescent layer comprises a mixture of 100 parts, by weight, of an electroluminescent phosphor, 30 to 50 parts, by weight, of a liquid crystal and 10 to 40 parts, by weight, based on the sum of the parts of the electroluminescent phosphor and the liquid crystal, of an inorganic binder.

. l BBQ-"345 SR 1 T RR 3 775 631 l [11] 3,775,631 F H v! s s Nov. 27, 1973 [54] DISPERSION TYPE 3,560,784 2/1971 Steele 3l3/l08 A ELECTROLUMINESCENT ELEMENTS [75] Inventor: Mitsuaki Morikawa, Mie Prefecture, Prim ry -James a rence Japan Assistant ExaminerC. E. Church Y l Chtt' k [73] Assrgnee: lse Electronics Corporation, Mic Attorney C 3rd ey l et a] Prefecture, Japan [22] Filed: Oct. I1, 1972 [57] ABSTRACT PP 296,559 In a dispersion type electroluminescent element comprising a pair of electrodes and an electroluminescent [30] Foreign Application priority Data layer sandwiched between the electrodes and includ- 0 t H 197 J 46/79991 ing an electroluminescent phosphor dispersed in an apan organic or inorganic binder, the luminescent layer [52] Us Cl 313/108 A 350/160 LC 350") LC comprises a mixture of 100 parts, by weight, of an [51] 29/18 electroluminescent phosphor, 30 to 50 parts, by [58] n .ld 3131/1023 A weight, of a liquid crystal and 10 to 40 parts y e at weight, based on the sum of the parts of the electrolu- [56] Ref r nee Cited minescent phosphor and the liquid crystal, of an inore e s ganic binder. UNITED STATES PATENTS 3,306,770 2/1967 Klug 313/108 A 2 Claims, 2 Drawing Figures 4 m I I I I. f/

'PATENTED 2 3,775,631

PRIOR ART DISPERSION TYPE ELECTROLUMINESCENT ELEMENTS BACKGROUND OF THE INVENTION This invention relates to a luminous display element utilizing a phosphor for electroluminescence (EL), and more particularly to a dispersed type electroluminescence display element.

Electroluminescence display elements are generally classified into a vapour deposited film type EL cell and a dispersed type EL cell in which an electroluminescent phosphor is dispersed in a suitable organic or inorganic binder. The organic binder includes castor oil, glycerine, a cetal resins, epoxide resins, methymethacrylate polyester, polyethylene, polystyrene, cyanoethyl cellulose, etc., whereas the inorganic binder includes ferroelectric materials, such as electroluminescent enamel, barium titanate, R chelle salt, potassium phosphate hydroxide and lead titanate.

As shown in FIG. 1, the conventional dispersed type EL cell comprises a metal electrode 1, a transparent electrode 2, an electro-luminescent display element 3 comprising a mixture of an electroluminescent phosphor and an organic or an inorganic binder of the type described above, spacers 4 made of a synthetic resin and interposed between electrodes 1 and 2 for defining a gap between the two electrodes 1 and 2 for accommodating the electroluminescent display element 3 and an insulator film interposed between electrode 2 and luminescent display element 3 for the purpose of preventing insulation breakdown. The organic or inorganic binder should satisfy the following requirements. (a) It can be suitably admixed with the electroluminescent phosphor. (2) It should not react chemically with the electroluminescent phosphor. (3) It can firmly fix the electroluminescent phosphor. (4) It should have an excellent insulating property. (5) It's aging with time should be small. (5) It should have a high breakdown voltage against impressed voltage and (7) its dielectric constant is large. Actually, however, the organic binders can not satisfy the requirements 3 to 7 and the inorganic binder can not satisfy the requirement 1. The provision of spacers 4 for defining a gap between the electrodes and insulator film 5 for preventing insulation breakdown increases the number steps of fabrication and the cost of manufacturing.

SUMMARY OF THE INVENTION It is an object of this invention to provide a novel dispersed type electro luminescence display element which has a simple construction and can eliminate the disadvantages described above.

According to this invention there is provided a scattered type electroluminescent display element comprising a pair of opposed electrodes and an electroluminescent layer disposed between the electrodes, the electroluminescent layer comprising a mixture of I00 parts, by weight, of an electroluminescent phosphor, 30 to 50 parts, by weight, of a liquid crystal and 10 to 40 parts, by weight, based on the sum of the parts of the electroluminescent phosphor and the liquid crystal, of an inorganic binder. I

The liquid crystal is characterized in that (I) it has an extremely high insulation strength, (2) it can be thoroughly admixed with and dispersed in the electroluminescent phosphor at any ratio, (3) it can act as an organic binder which is stable over severel thousands hours without aging (4) it is transparent of slightly clouded so that it can efficiently emanate luminous light, (5) it establishes a dipole moment when impressed with a voltage so as to apply electric field efficiently across the phosphor and (6) it has a relatively high dielectric constant. On the other hand the inorganic binder is advantageous in that (1) it has an extremely high dielectric constant and (2) it can reflect electroluminescent light where it is white.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing FIG. 1 shows a sectional view ofa prior art dispersion type electroluminescent cell and FIG. 2 is a sectional view of an improved dispersion electro-luminescent cell embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 shows one embodiment of this invention comprising electrodes 11 and 12, at least one of them being transparent, and an electroluminescent layer 13 comprising the above described mixture of an electroluminescent phosphor, a liquid crystal and inorganic binder. The liquid crystal shows liquid state in the room temperature and high insulating characteriscs. The liquid crystal which is used in the present invention for example, is MBBA (Methoxy Benzilyden Buthyl Aniline), EBBA (Ethoxy Benzilyden Buthyl Aniline) or a mixtre thereof.

In operation, an operating voltage is applied across electrodes 11 and 12 to apply an electric field across the electroluminescent layer. Accordingly, the luminous centers of the phosphor are excited. When the polarity of the applied field is reversed, the excited electrons recombine with the luminous centers to emanate electroluminescence characteristic of the electroluminescent phosphor used. The light is seen through the transparent electrode.

As above described, this invention utilizes the advantages of both the liquid crystal and inorganic binder. Consequently, it is not necessary to use the insulator film for preventing insulation breakdown so that it is possible to increase the brightness of the electroluminescent element, and to simplify the construction and fabrication of the element. Fruther the operation of the electroluminescent element of this invention is stable over a long period without aging.

What is claimed is:

1. In a dispersion type electroluminescent element of the type comprising a pair of electrodes and an electroluminescent layer sandwiched between said electrodes, said layer including an electroluminescent phosphor dispersed in an organic or inorganic binder, the improvement wherein said electroluminescent layer comprises a mixture of parts, by weight, of an electroluminesccnt phosphor, 30 to 50 parts, by weight, of l liquid crystal and 10 to 40 parts, by weight, based on the sum of the parts of said electroluminescent phosphor and said liquid crystal, of an inorganic binder.

2. The electroluminescent element according to claim 1 wherein said liquid crystal is selected from the group consisting of MBBA (Methoxy Benzilyden Buthyl Aniline), EBBA (Ethoxy Benzilyden Buthyl Aniline) and a mixture thereof. 

2. The electroluminescent element according to claim 1 wherein said liquid crystal is selected from the group consisting of MBBA (Methoxy Benzilyden Buthyl Aniline), EBBA (Ethoxy Benzilyden Buthyl Aniline) and a mixture thereof. 